Flour treatment method

ABSTRACT

The invention relates to a method to sterilise flour to reduce the enzymatic activity within the flour as well as to reduce microbial decontamination of the flour and thereby minimising pasting of starch and preserving the flour in its native form. The invention also relates to the flour obtained by the method and an aseptically packed fluid mixture comprising the flour and a method to produce the aseptically packed fluid mixture.

FIELD OF THE INVENTION

The invention relates to a method to sterilise flour to reduce theenzymatic activity within the flour as well as to reduce microbialcontamination of the flour and thereby minimise pasting of the starchand maintaining the flour in its native form. The invention also relatesto the flour obtained by the method and an aseptically packed fluidmixture comprising the flour and a method to produce the asepticallypacked fluid mixture.

BACKGROUND OF THE INVENTION

When grains are grown in the fields, the final quality is very dependenton the climate. If bad weather persists, and/or it is very windyso-called layers are produced, which often result in that the grainspossess a high diastatic activity. High diastatic activity means thatenzymes are produced/synthesised within the grains, which breaks downthe starch during the use of the grain within the food industry orbaking in households.

One way to screen the quality of the grains after harvest is to use theso-called Falling Number, which is a number obtained by a method whichmeasures the diastatic activity. A high Falling-Number implies lowdiastatic activity and vice-versa, which means that, grains obtaining ahigh Falling-Number has a high enzymatic activity and has been growingunder bad conditions in the field. When high enzyme activity isprevalent, the microbial contamination level in the grains are mostoften high. Grains possessing high diastatic activity and a highmicrobial contamination level is not suitable for the production offlour to be used in food products, but is used instead for theproduction of animal feed, which reduces the economic value for thefarmer.

Heat treatment of flour is one way to reduce enzymatic activity.However, high heat treatments result in colour changes and taste changesof the flour, Furthermore, reduction of the microbial level is notsatisfactory since the use of heat treatment has to be conducted in asufficiently dry environment to avoid problems such as gelatinisation ofstarch within the flour. If this happens, the basic properties of theflour become altered. It is previously known that a reduction ofmicrobes takes place more efficiently in the presence of water. Forexample, 10 minutes at 121° C. in a humid environment is used topreserve sterility, while 3 hours at 180° C. is necessary to effect adry sterilization. Such high temperatures in flour result in anunfavorable strong dextrinisation (i.e., dry heat degradation) of starchfraction, as well as changes in smell and colour.

Another method to reduce the number of bacteria is to irradiate withγ-rays. However, from the consumer's viewpoint, the technology isintuitively negative, which has resulted in negligible use of thismethod in industry, even though it is permitted within the EU and by theSwedish Food Agency to be used to reduce the bacterial number in spices.Products may also be sterilised by other known techniques like,fumigation using, for example, ethylene oxide, propylene oxide andsulphur dioxide. The first two mentioned gases lead to formation oftoxic products, such as chlorohydrins, which is why the method usingfumigation is forbidden in more and more countries all over the world.Sulphur dioxide is very toxic, and forms a hazard to the industrialstaff who have to perform the fumigation. A common example of the use ofthis method is the conservation of different fruitpulp masses.

Surfaces have, since the beginning of the 1900's, been disinfected with70% (volume/volume) ethanol, both within healthcare and the foodindustry. Ethanol of this strength has proven to be effective towardsvegetative bacteria, but insufficiently effective towards bacteria inthe spore stages, which survive the treatment. Since these spores evensurvive the heat treatment to which the flour is exposed to during thebaking process. This method is far from satisfactory. At the same time,the use of ethanol does not contribute to a reduction of excessiveenzymatic activity in the flour.

The food industry has for a long time been trying to sterilise andaseptic pack mixtures based on flour suspended in a liquid to enable theconsumers to bake themselves without any prior steps of preparation ofthe mixture. However, problem arises when the sterilisation requiresheat treatment in a water containing environment. Such a treatment isnot possible to be used on a mixture of flour and liquid since theamount of flour needs to be maintained at a high level to obtain a solidproduct after baking. Additionally, if the mixture containing flour andliquid is heat treated, the baking will take place already during theheat treatment (sterilisation), and the equipment used for sterilisationwill be plugged up by baked (expanded) products. One way to solve theproblem is to use a low careful heat treatment, to achieve,pasteurisation of the mixture without changing the properties of thestarch within the flour. The temperature to be used in such a methodshould not be higher than 60° C., since at this temperature, the starch,at least in wheat, which is the most commonly used flour product for thepreparation of mixtures, begins to exhibit stickiness, i.e., obtainpasting qualities. Additionally, the product has to be placed cold suchas in a refrigerator prior to use, which gives the product a verylimited lifetime.

The present invention provides a new method, which enables thepossibility to sterilise flour as it is in dry conditions. The method isalso an effective method to treat without changing the properties of theflour. The method further reduces the enzymatic activity within theflour and eliminates unfavourable microbes present within the flour,including spores.

Additionally the invention provides a new aseptically packed fluidmixture, in which the flour and the liquid are mixed and may be storedin room temperature prior to use.

SUMMARY OF THE INVENTION

The invention relates to a method to sterilise flour, in which theenzymatic activity is reduced and microbes are eliminated, withoutallowing the starch to gelatinise and become sticky. Thereby, it becomespossible to use flour, which has been growing under unfavourableconditions for the human consumption. Flour, which today either arediscarded or used as animal feed.

According to a first aspect the invention relates to a method tosterilise flour, comprising the steps of providing the flour obtainedfrom grain, mixing the flour with alcohol, heating the mixture of flourand alcohol, under closed conditions, to a temperature above 78° C.; andobtaining a flour product having a reduced enzymatic activity and areduced/eliminated microbial contamination withoutpasting/gelatinisation of the starch within the flour and the productobtained therefrom.

According to a second aspect the invention relates to an asepticallypacked fluid mixture, which may be stored at room temperature prior touse and a method to produce the aseptically packed fluid mixture. Theaseptically packed fluid mixture comprises a flour product sterilised ina manner described above and a sterile fluid phase, wherein the starchof the flour remains in a non-gelatinised condition after packaging.

The natural occurring gelatinisation properties of the starch aremaintained after the method to sterilise the flour.

DETAILED DESCRIPTION OF THE INVENTION

Method for Sterilisation

The invention relates to a method for sterilisation of flour in whichalcohol, such as ethanol is heated to a temperature, which is above theboiling point for the alcohol/water azeotrope. The method, result in apowerful increase of alcohol's disinfectant effect, so that evenbacteria in the spore-forming stages are destroyed/eliminated. By such amethod it then becomes possible to obtain complete sterility at a lowertemperature, i.e., a milder treatment as compared to when water is usedin the sterilisation step. Additionally the enzyme activity iscompletely eliminated after the treatment and yet, surprisingly, thestarch within the flour remains intact after the treatment.

The flour obtained from grain, to be sterilised is mixed withalcohol/ethanol. The quantity of alcohol, which is used is adjusted sothat the flour is always in the form of a powder and may be less than20% (weight/volume). After the flour and the alcohol have been mixed andis more or less homogenous distributed, the mixing tank is sealed andthe heat treatment starts. It is important that the tank is so tightlysealed that pressure is obtained from the quantity of alcohol, which isevaporated, when the boiling point of the alcohol/water azeotrope (78°C.) is reached. In this way, there is no ethanol loss, and it becomespossible to reach temperatures above the boiling point of the azeotrope.It is through the increase of the temperature that the stronglyincreased disinfectant effect is obtained.

Depending on the pressure resistance of the tank to be used, theflour/alcohol mixture may be treated to a temperature from about 78° C.to about 120° C. An increase in the temperature result in general in adecrease in the time necessary to be used. Heating to 95° C., result ingeneral to a complete sterility within 5-30 minutes. The pressure insuch a case is often less than 1.5 bars.

The sterilisation may be performed from about 1 second to about 5 hoursusing from about 1 to about 5 bars, depending on the microbiologicalquality of the starting material.

When the sterilisation has been finalised, the pressure is released,often through the opening of a valve, which may be connected to acondenser, and the evaporated ethanol may then be used again in afurther sterilisation cycle. Through this flashing process the productexperiences a rapid cooling down to the azeotrope's boiling point. Whenthe pressure equalise is restored, a vacuum may be applied, if desired,to eliminate residuals of the ethanol. This stage is not a necessity,since small amounts of ethanol are not toxic and will escape laterduring baking of the product, before consumption of the food product.

A number of different commercially available equipments may be found,which are directly suited for use in the described flour treatmentprocess, such as for example, Vakuum Nauta-dryer or Ross conicalvertical blender/dryer.

The sterilisation method may be used for all kinds of grains, such asmaize and rice. It also includes cereals, such as wheat, oats, barleyand rye.

Aseptically Packed Fluid Mixture and Method to Produce the Mixture

Additionally the invention relates to an aseptically packed fluidmixture comprising the flour product produced by the above mentionedmethod and at least one fluid phase, wherein the starch of the flourremains in a non-gelatinised condition after packaging. The fluid phaseis described in detail below. Such an aseptically packed fluid mixtureis in favour since there is no need to store the product in a fridgeprior to use.

Production of the Aseptically Packed Fluid Mixture

The Flour Product

The flour product will be sterilised using the above, mentioned methodin a separate process line from the fluid phase. After sterilisation theflour product will be kept in a sterile compartment until being mixedwith the sterile fluid phase.

The Fluid Phase

The ingredients, which comprise the fluid phase, which are to besterilised are separately sterilised. One way is to suspend theingredients in a tank and then sterilise the tank. The sterilisation maybe performed either on a batch-to-batch basis, or on a continuous basis.The continuous process is preferred since it would be possible then touse the known HTST/UHT technique, implying that through the use of hightemperatures, only a very short exposure time (seconds to minutes,depending on the end temperature) is required. This, results in bettercolour, taste and smell properties of the sterilised liquid/fluid phaseand gives a higher final quality to the sterilised product.

Mixture Preparation

The separately sterilised flour product and fluid phase are then mixedwith each other using defined amounts of the flour and the fluid. Oneway is to weight and combine them according to a recipe, and then mixthem under aseptic conditions until the mixture is homogenous. Toachieve homogeneity, the mixture may be homogenised using traditionalfood production equipment, which is well known for a person skilled inthe art. The weighting may be performed using weighing cells supplied inthe sterile mixing tank.

Either the flour product is added to the fluid phase or the opposite.The choice of the order of mixing depends on the practical conditionsduring the preparation process.

The mixing may either be performed under sterile conditions oraseptically.

Packaging

All forms of sterile packages, which are filled through “aseptictechnologies” or under sterile conditions may be used for the mixturesnamed in this invention. There is, however, a preference for packagesthat have some airspace in the top parts of the packages so that it ispossible to shake the product and in this way, disperse the sedimentedstarch particles. One way to avoid sedimentation is the use of asuitable hydrocolloid, such as xanthan gum or carrageenan within themixture. Additionally synthetic, semisynthetic hydrocolloids or mixturesthereof may be used.

Examples of aseptically packed fluid mixtures includes, pancake mixes,waffle mixes, mixtures for batters as well as cake mixtures for eg.,spongecakes, cakes and muffins.

Even if some of the examples are based on pancakes, this does notexclude the possibility to vary the ingredients or to add extracomponents.

By varying the content of the flour, adding eggs to the ingredient list,etc., a list of different products may result—for example, wafflemix,cake mix, batters for pancakes and similar, which, of course, areimplied as included within the framework of the present invention.

EXAMPLES Example 1

To flour obtained from a highly infected grain having a Falling-Numberof 80, was bacteria added in the form of a freeze-dried vegetativelactic acid bacteria culture. The added inoculum was approximately 10⁸bacteria/g flour. The water content in the flour was 13%.

500 g of the flour was placed in a pressure reactor with a powderstirrer. 50 ml 95% (volume/volume) ethanol was nozzled in a fine dimwhile the flour was mixed. When the mixture was homogenous, the reactorwas sealed and the heating process initiated.

The mixture was heated to 95° C. and maintained at that temperature for20 minutes. Then, the mixture was flash-cooled resulting in a fasttemperature drop to 80° C. A minor vacuum was applied to remove theleftover ethanol. When all the ethanol was gone, the flour was cooleddown to room temperature before the flour was removed from the reactor.The flour retained its powder characteristics.

The moisture content in the sterilised flour was, after treatment, 12%,which is an indication that a minor part of the moisture of the flourwas removed during the vacuum treatment.

Example 2

The flour obtained from example 1 was examined under polarised light ina microscope (a method to see if the starch has gelatinised or not) andwas found to have retained its birefringence properties.

Example 3

Analysis of the Falling-Number after treatment showed that the value hadincreased to 285, which is considered to be optimal for a breadbakingflour. This shows that the diastatic activity has ceased.

Example 4

Comparison in a Brabender Amyloviscograph (an analytical instrument tostudy starch gelatinisation and viscosity) at 7% dry matter showed that,for untreated flour, a straight line plot was obtained, implying that noincrease in viscosity could be observed. This was because the starchdegrading enzymes decomposes the starch resulting in the absence ofviscous properties.

Analysis of the treated flour from example 1 showed a strong pastyprocess, which was comparable to traditional flour possessing a highFalling-Number. This shows that the starch degrading enzymes in theoriginal flour have been eliminated.

Example 5

Microbial analysis of the treated flour showed absence of microbialcontamination for all dilution levels (smallest dilution was < 1/10 ofthe original sample). The analysis includes the total aerobic count,coliforma enterobacteria as well as yeast and moulds using conventionalmethods well-known for a person skilled in the art.

Example 6

The flour from example 1 was tested against a conventional householdflour in a standard pancake recipe. No negative effects of the abovementioned treatment were detected during the bakingf process. During thepreparation of the pancake mixture, it was found easier to prepare amixture using the flour from example 1. The standard flour (wheat flourof commercial quality for baking purposes in industry and household) wasfound to form more clumps (or form lumps more easily).

Example 7

50 kg of flour with a total bacterial count of 20,000/g was loaded andto this 5 liters 95% (volume/volume) ethanol was added in a large doublemantle vacuum tumbling container. The mixture was heated to 95° C.Since, the heating time to reach 95° C. was so much longer than theexperiment described in example 1, the process was stopped immediatelywhen the required temperature was reached. The ethanol was removed fromthe container and the pressure released. Samples for bacterial analysiswere taken.

Example 8

The results from the microbiological tests from the trial in example 7showed that all the tests were free from growths. No spores could bedetected.

Example 9

In a tank 100 kg skim milk powder, 4.13 kg salt, 47.5 kg cooking oil and933 liters of water were suspended and pumped through an indirecttubular heat exchanger and heated to 127° C. and held constant at thattemperature for 60 seconds. The mixture was then pumped further to atube cooler and cooled to 20° C.

In a pressure proof tank 125 kg wheat flour was added and 12.5 liter 95%(volume/volume) ethanol streamed in through a nozzle during the mixingprocess. The tank was then closed and heating was started. When atemperature of 95° C. was reached, the temperature was held constant for20 minutes. Then the positive pressure of the alcohol was released andthe flour cooled down to 50° C.

The sterilised flour was blended aseptically with 415 kg of thesterilised liquid phase described above to reach a total weight of 540kg in the mixture.

The mixture was pumped through a milk homogeniser to a sterile tankbefore the filling machine.

The product was packed in 1-liter Tetra packages and an asepticallypacked fluid mixture consisting of a pancake mix was produced.

Example 10

Microscopy of the packed pancake mix showed that the starch componentwas intact and kept its properties of birefringence in plane polarisedlight, indicating that the crystal structure is unchanged after the heattreatment.

Example 11

Microbial analysis were performed by cultivation at 3 differenttemperatures, 25, 40 and 55° C., immediately after production, and afterpre-incubation in an incubator at 40° C. for 2 days. All samples werefree from growth. This shows that the product is sterile.

Example 12

One of the packages produced in EXAMPLE 9, was baked after 2 days andanother one after 14 days storage at room temperature. No difference inthe properties of the product could be observed. Both gave well-bakedpancakes as a result having a excellent taste.

1. A method to sterilise flour, comprising the steps OF: a) providingthe flour obtained from grain; b) mixing the flour with alcohol; c)heating the mixture of flour and alcohol, under closed conditions, to atemperature above 78° C.; and d) obtaining a flour product having areduced enzyme activity and microbial contamination withoutgelatinisation of the starch part of the flour.
 2. The method accordingto claim 1, wherein the alcohol content in b) is less than 20%(WEIGHT/VOLUME) of the total mixture.
 3. The method according to claim1, wherein the temperature in c) is between 78° C. and 120° C.
 4. Themethod according to claim 1, wherein the temperature in c) is maintainedfrom about 1 second to about 5 hours.
 5. The method according to claim1, wherein the closed conditions in c) is under pressures held betweenfrom about 1 to about 5 bars.
 6. The method according to claim 1,wherein the flour is obtained from maize, rice and cereals such aswheat, oats, barley and rye.
 7. A flour product obtained by the methodaccording to claim
 1. 8. An aseptically packed fluid mixture comprising;a) the flour product according to claim 7 and b) a sterile fluid phase,wherein the starch of the flour remains in a non-gelatinised conditionafter packaging.
 9. The aseptically packed fluid product according toclaim 8, wherein the product comprises a hydrocolloid such as xanthangum or carragenan, synthetic, semisynthetic hydrocolloids or mixturesthereof.
 10. A method to produce an aseptically packed fluid accordingto claim 8 comprising the steps OF: a) providing and sterilising a fluidphase; b) providing and sterilising flour separately from the fluidphase; c) Mixing the fluid phase and the flour product aseptically orsterile to a fluid mixture; and d) Aseptically or sterile pack the fluidmixture, where the starch of the flour remains in a non-gelatinisedcondition after the treatment.
 11. The method according to any of theclaims 10, wherein a hydrocolloid such as xanthan gum or carragenan,synthetic, semisynthetic hydrocolloids or mixtures thereof is added tothe fluid mixture under c).